Rio Alto Drills 314 m @ 0.7 g/t Au at La Arena

VANCOUVER, BRITISH COLUMBIA--(Marketwired - May 15, 2014) -Rio Alto Mining Limited ("Rio Alto" or the "Company") (TSX:RIO)(NYSE:RIOM)(LMA:RIO)(DBFrankfurt:MS2) is pleased to report assay results from 19 reverse circulation ("RC") drill holes within and around the Calaorco Pit at the Company's La Arena Gold Oxide Mine located in La Libertad, northern Peru.

Reference is made to the 2014 oxide gold Reserve Pit which is detailed in the La Arena Project Technical Report with an effective date of December 31, 2013, prepared on behalf of the Company by Mining Plus Peru S.A.C. (the "December 2013 Report"), a copy of which is available under the Company's SEDAR profile at www.sedar.com.

Rio Alto acquired the La Arena Gold Project in mid-2009 from IAMGOLD with the objective of bringing the mine into production as rapidly as possible. Twenty months later, the first gold bar at La Arena was poured and since then the Company has produced approximately 550,000 ounces of gold. The principal focus during the first two years of project ownership was to achieve gold production to allow the Company to generate cash flow and fund further expansion and development of the project from this cash flow. Exploration drilling was deferred during this period and only commenced after positive cash flow started to be generated by the project in early 2012.

Since 2012, oxide drilling has resulted in the gold oxide reserve increasing from 821,000 ounces at the beginning of 2011 to 1,056,000 ounces at the beginning of 2014 with approximately 500,000 ounces having been produced during the first two and half years of production. This represents an increase of approximately 780,000 ounces since mining commenced at La Arena.

The following results are from the first 19 RC holes drilled at Calaorco during 2014 with 13 out of the 19 holes intersecting gold mineralization above the mining cutoff grade. These drill holes were within ("Inside") and extended outside or below ("Outside") the 2014 gold oxide Reserve Pit.

The results of the recent drilling program demonstrate that a large amount of oxide brecciated sandstone mineralization (the main mineral type at La Arena) lies outside the 2014 Reserve Pit. The results are very encouraging and indicate the potential to increase oxide gold resources and reserves and the possibility of extending mine life beyond 2019.

A total of 14,200 metres of RC drilling is currently planned to be completed during 2014, in and around the Calaorco Pit. The Company´s geologists will interpret the data generated by this drilling program, once it is completed, with the objective of calculating an updated resource and reserve estimate for the gold oxide mineralization at La Arena. Management expects that this drilling program has the potential to allow positive changes to be made to the resource block classification, define new resource blocks and given that the deposit is open to the northwest and at depth, identify new areas to test in order to further increase resources and reserves in the future. The updated resource and reserve estimate for the gold oxide mineralization at La Arena is expected to be released in Q1, 2015.

Drill Results

References to the comments in the following table refer to intercepts within ("Inside") the 2014 Reserve Pit or drill hole intercepts that extended outside or below ("Outside") the 2014 Reserve Pit. A map illustrating drill hole locations and selected drill hole cross sections related to this press release may be accessed by following this link.

Hole ID

From

To

Interval

Au g/t

Ag g/t

Cu ppm

Comments

CA-R14-001

Not significant Intercepts

CA-R14-002

Not significant Intercepts

CA-R14-003

116

176

60

0.31

1.97

77

Inside Reserve Pit

Including

116

134

18

0.72

3.56

151

Outside Reserve Pit

CA-R14-003

190

218

28

0.44

1.04

176

Outside Reserve Pit

CA-R14-004

6

26

20

0.14

0.13

28

Inside Reserve Pit

CA-R14-004

92

110

18

0.15

0.21

28

Inside Reserve Pit

CA-R14-004

120

168

48

0.38

0.92

36

Outside Reserve Pit

CA-R14-005

Not significant Intercepts

CA-R14-006

Not significant Intercepts

CA-R14-007

12

94

82

0.62

0.62

101

Inside Reserve Pit

CA-R14-007

110

138

28

0.19

0.32

16

Outside Reserve Pit

CA-R14-007

150

164

14

0.16

0.33

44

Outside Reserve Pit

CA-R14-007

202

276

74

0.42

0.51

83

Outside Reserve Pit

Including

254

276

22

1.06

1.30

146

Outside Reserve Pit

CA-R14-008

Not significant Intercepts

CA-R14-009

30

90

60

0.18

0.36

52

Inside Reserve Pit

CA-R14-009

112

272

160

0.40

0.71

68

Outside Reserve Pit

Including

254

268

14

1.56

0.73

113

Outside Reserve Pit

CA-R14-010

Not significant Intercepts

CA-R14-011

Not significant Intercepts

CA-R14-012

Not significant Intercepts

CA-R14-013

28

44

16

0.29

0.73

16

Inside Reserve Pit

CA-R14-013

66

76

10

0.23

0.74

17

Inside Reserve Pit

CA-R14-013

108

118

10

0.16

0.32

23

Outside Reserve Pit

CA-R14-013

132

150

18

0.18

0.32

21

Outside Reserve Pit

CA-R14-013

166

248

82

0.25

0.26

66

Outside Reserve Pit

Including

166

188

22

0.46

0.39

163

Outside Reserve Pit

CA-R14-014

18

56

38

0.20

0.13

60

Inside Reserve Pit

CA-R14-014

64

118

54

0.70

0.55

55

Inside Reserve Pit

Including

82

86

4

1.26

1.15

24

Inside Reserve Pit

Including

102

108

6

4.10

1.57

238

Inside Reserve Pit

CA-R14-014

156

162

6

1.93

0.87

226

Outside Reserve Pit

CA-R14-014

152

222

70

0.35

0.34

50

Outside Reserve Pit

Including

206

210

4

1.12

0.30

133

Outside Reserve Pit

CA-R14-014

232

282

50

0.74

0.19

88

Outside Reserve Pit

Including

266

280

14

1.90

0.24

233

Outside Reserve Pit

CA-R14-014

294

304

10

0.15

0.22

11

Outside Reserve Pit

CA-R14-015

0

8

8

0.29

0.10

113

Inside Reserve Pit

CA-R14-015

22

336

314

0.70

0.21

113

Inside Reserve Pit

Including

22

26

4

2.15

0.10

432

Inside Reserve Pit

Including

72

86

14

0.96

0.21

43

Inside Reserve Pit

Including

96

110

14

2.18

0.53

72

Outside Reserve Pit

Including

170

336

166

0.80

0.24

137

Outside Reserve Pit

CA-R14-016

0

230

230

0.97

0.72

78

Inside/Outside Reserve Pit

Including

0

36

36

2.75

1.11

28

Inside Reserve Pit

Including

156

230

74

0.67

0.70

123

Outside Reserve Pit

Including

214

230

16

1.38

1.99

242

Outside Reserve Pit

CA-R14-017

0

164

164

0.45

0.17

80

Inside/Outside Reserve Pit

Including

40

48

8

1.72

0.23

372

Inside Reserve Pit

Including

82

94

12

1.69

0.15

269

Inside Reserve Pit

CA-R14-017

206

226

20

0.23

0.10

17

Outside Reserve Pit

CA-R14-018

102

210

108

0.20

0.80

32

Inside Reserve Pit

Including

114

128

14

0.82

1.63

73

Outside Reserve Pit

CA-R14-019

30

78

48

0.72

0.68

69

Inside Reserve Pit

Including

38

68

30

1.04

0.67

94

Inside Reserve Pit

CA-R14-019

88

138

50

0.21

0.65

22

Inside Reserve Pit

CA-R14-019

172

210

38

0.49

1.22

211

Outside Reserve Pit

Including

182

192

10

0.85

1.78

80

Outside Reserve Pit

CA-R14-019

224

241

17

0.32

0.35

32

Outside Reserve Pit

Sampling of the reverse circulation drilling and sample preparation were performed by Rio Alto personnel and were carried out under strict protocols recommended in the NI 43-101 Technical Report dated July 31, 2010 prepared by Coffey Mining Pty Ltd for the Company (the "Report"). Samples were taken every 2m and split in half to yield seven to ten kilogram samples. Drill sample recovery was generally in excess of 90%. Rio Alto has a rigorous QA/QC program over the chain-of-custody of samples and the insertion of blanks, duplicates, and certified reference standards in each batch of samples. Samples were shipped to CERTIMIN in Lima where they were dried, crushed, pulverized, and assayed. All gold assays were obtained by standard 50g fire assaying with AA finish. All silver assays reported in the press release were obtained by Aqua-Regia dissolution followed by ICP measurement. CERTIMIN is an ISO 9001:2000 certified laboratory.

Phase II Update

Good progress is being made in respect to the completion of the feasibility study for the Phase II copper/gold project at La Arena. On January 6, 2014, the Company announced that it had received formal notification from the Ministry of Energy and Mines of Peru that approval had been given for modifications to its Environmental Impact Study (EIA) for the La Arena Project Gold Oxide Mine. This EIA modification allows Rio Alto to apply for permits for a future Phase II open pit sulphide mine, construct an 18,000 tonne per day copper/gold concentrator, expand the current waste dump facilities to accommodate sulphide waste and to use the Calaorco Pit for tailings deposition once open pit oxide reserves are exhausted. However, the recent increase in the size of the adjacent gold oxide deposit and possible expansion of the oxide resources and reserves as a consequence of the ongoing drill program, has meant that the general layout of the Phase II infrastructure needs to be revised. It is important that none of the Phase II infrastructure, such as process plant, conveying systems, stockpiles and waste dumps are impeding the possible future expansion of the oxide mine and its associated infrastructure. This revision of the general layout has meant that the completion of the feasibility study will be delayed until later in the year. Current estimates for timing are sometime in Q4, 2014.

"We are all excited at the results coming out of our current oxide drilling program at La Arena. It is hoped that the program underway can increase the size and life of the gold oxide mine and provide our technical team with a better understanding of what the optimal general layout for Phase II should be. La Arena has been a great project from the outset and continues to evolve positively for all stakeholders involved," commented Alex Black, President & CEO.

Mr. Enrique Garay, MSc. P.Geo (AIG Member), Vice President Geology of Rio Alto, is the Qualified Person (as defined by NI 43-101) responsible for managing the Company's exploration programs and disclosure of drilling results. Mr. Garay has read and approved the scientific and technical information in this news release.

For additional information regarding La Arena Project please refer to the December 2013 Report prepared on behalf of the Company by Mining Plus Peru S.A.C., a copy of which is available on the Company's SEDAR profile at www.sedar.com.

Forward-Looking Statements

Certain statements contained herein constitute forward-looking statements, most particularly the potential to increase the resource and reserve estimate of the gold oxide mineralization at La Arena Project, the timing for the completion of an updated resource and reserve estimate for the gold oxide mineralization at La Arena Project, to extend the life of La Arena Gold Oxide Mine and the timing for the completion of a feasibility study for the La Arena copper/gold sulphide project. All statements included herein, other than statements of historical fact, are forward-looking information and such information involves various risks and uncertainties. Rio Alto believes the expectations reflected in these forward looking statements are reasonable but no assurance can be given that these expectations will prove to be correct and such forward-looking statements in this press release should not be unduly relied upon. A description of assumptions used to develop such forward-looking information and a description of risk factors that may cause actual results to differ materially from forward-looking information can be found in Rio Alto's disclosure documents on the SEDAR website at www.sedar.com. Forward-looking statements included in this press release are made as of the date of this press release and Rio Alto disclaims any intention or obligation to update or revise any forward-looking statements, whether as a result of new information, future events or otherwise, except as expressly required by applicable securities legislation.